At least two different monomers can be polymerized in the same polymerization system so as to generate a copolymer having those different monomer units arranged as repeating units in one polymer chain, and the copolymer thus obtained can be classified into a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer, depending on the arrangement of the monomer units. However, no report has been made on the arrangement of monomer units in polymerization reaction of a conjugated diene compound and a non-conjugated olefin.
For example, JP 2000-154210 A (PTL 1) discloses a catalyst for polymerization of a conjugated diene, the catalyst including a group IV transition metal compound which has a cyclopentadiene ring structure, in which an α-olefin such as ethylene is exemplified as a monomer copolymerizable with the conjugated diene. However, no reference is made on the arrangement of monomer units in the copolymer. Further, JP 2006-249442 A (PTL 2) discloses a copolymer of an α-olefin and a conjugated diene compound, but no reference is made on the arrangement of monomer units in the copolymer. Further, JP 2006-503141 A (PTL 3) discloses an ethylene-butadiene copolymer synthesized by using a catalytic system consisting of a specific organometallic complex, but merely describes that the butadiene as a monomer is inserted in the form of trans-1,2-cyclohexane into the copolymer, without making any reference to the arrangement of monomer units in the copolymer, and no reference is made to a rubber manufactured by using a random copolymer having randomly arranged monomer units of a conjugated diene compound and of a non-conjugated olefin, so as to obtain an excellent heat resistance and crack growth resistance.
In addition, JP 11-228743 A (PTL 4) discloses an unsaturated elastomer composition composed of an unsaturated olefin-based copolymer as a random copolymer and a rubber. However, the copolymer includes a plurality of structures having not only 1,4 bonds and 1,2 bonds (including 3,4 bonds) but also three members and five members, and thus the arrangements thereof are unclear.
Further, although PTL 4 actually exemplifies a ternary copolymer, no description is given of an example of a binary copolymer such as an ethylene-butadiene copolymer.
In addition, no reference is made to the crack growth resistance of an unsaturated elastomer composition including the random copolymer, and therefore it is unclear about the property.
That is, JP 11-228743 A (PTL 4) does not describe a rubber manufactured by using a random copolymer having randomly arranged monomer units of a conjugated diene compound and of a non-conjugated olefin, so as to obtain an excellent heat resistance and crack growth resistance.